A pilot signal, preamble, or reference signal are commonly used for communication systems to enable the receiver to perform a number of critical functions, including but not limited to, the acquisition and tracking of timing and frequency synchronization, the estimation and tracking of desired channels for subsequent demodulation and decoding of information data, the estimation and monitoring of the characteristics of other channels for handoff, interference suppression, etc. Several pilot schemes can be utilized by communication systems, and typically comprise the transmission of a known sequence at known time intervals. A receiver, knowing the sequence only or knowing the sequence and time interval in advance, utilizes this information to perform the abovementioned functions.
A typical pilot format used in earlier orthogonal frequency division multiplexed (OFDM) systems is a “scattered pilot” format with pilots distributed in both time and frequency based on the expected maximum Doppler frequency and maximum delay spread, respectively. Scattered pilots might be viewed as the most general pilot format, but they are fairly difficult to specify. For example, it is less clear how to support a varying number of transmit antennas, how to optimize for low user speeds but allow insertion of additional pilots for high speeds, and how to avoid scattered pilot edge effects. Channel estimation is also in general more difficult because of the varied pilot locations in the frame and the sub-frame boundaries. For example, some simpler channel estimation techniques might not be available and more sets of interpolation filters may be necessary. In addition to being more complex, scattered pilots also consume power while decoding the control channel, even if there is no data for the receiver. Therefore, a need exists for a method and apparatus for pilot signal transmission in a communication system that alleviates the above-mentioned problems.